﻿/********************************************************
 *  ██████╗  ██████╗████████╗██╗
 * ██╔════╝ ██╔════╝╚══██╔══╝██║
 * ██║  ███╗██║        ██║   ██║
 * ██║   ██║██║        ██║   ██║
 * ╚██████╔╝╚██████╗   ██║   ███████╗
 *  ╚═════╝  ╚═════╝   ╚═╝   ╚══════╝
 * Geophysical Computational Tools & Library (GCTL)
 *
 * Copyright (c) 2023  Yi Zhang (yizhang-geo@zju.edu.cn)
 *
 * GCTL is distributed under a dual licensing scheme. You can redistribute 
 * it and/or modify it under the terms of the GNU Lesser General Public 
 * License as published by the Free Software Foundation, either version 2 
 * of the License, or (at your option) any later version. You should have 
 * received a copy of the GNU Lesser General Public License along with this 
 * program. If not, see <http://www.gnu.org/licenses/>.
 * 
 * If the terms and conditions of the LGPL v.2. would prevent you from using 
 * the GCTL, please consider the option to obtain a commercial license for a 
 * fee. These licenses are offered by the GCTL's original author. As a rule, 
 * licenses are provided "as-is", unlimited in time for a one time fee. Please 
 * send corresponding requests to: yizhang-geo@zju.edu.cn. Please do not forget 
 * to include some description of your company and the realm of its activities. 
 * Also add information on how to contact you by electronic and paper mail.
 ******************************************************/

#include "legendre.h"

double gctl::legendre_polynomials(size_t order, double x, bool derivative)
{
	//if (x > 1.0 || x < -1.0)
	//{
	//	throw gctl::runtime_error("The calculating position must be in [-1, 1]. From gctl::legendre_polynomials(...)");
	//}

	if (derivative == false)
	{
		if (order == 0) return 1.0;
		if (order == 1) return x;

		double n, p, p_1 = x, p_2 = 1.0;
        for (size_t i = 2; i <= order; i++)
        {
            n = (double) i - 1.0;
			p = (2.0*n + 1.0)*x*p_1/(n + 1.0) - n*p_2/(n + 1.0);
			p_2 = p_1; p_1 = p;
        }
		return p;
	}
	else
	{
		if (order == 0) return 0.0;
		if (order == 1) return 1.0;

		double n, p, p_1 = x, p_2 = 1.0;
		double pd, pd_1 = 1.0, pd_2 = 0.0;
		for (size_t i = 2; i <= order; i++)
		{
			n = (double) i - 1.0;
			p = (2.0*n + 1.0)*x*p_1/(n + 1.0) - n*p_2/(n + 1.0);
			pd = (2.0*n + 1.0)*(p_1 + x*pd_1)/(n + 1.0) - n*pd_2/(n + 1.0); 
			p_2 = p_1; p_1 = p;
			pd_2 = pd_1; pd_1 = pd;
		}
		return pd;
	}
}

void gctl::get_a_nm_array(int max_order, array<array<double>> &cs)
{
	int i, j;
	if (cs.size() != max_order)
	{
		cs.resize(max_order);
		for (i = 0; i < max_order; i++)
			cs[i].resize(i+1);
	}

	//向下列推计算
#pragma omp parallel for private(i,j) schedule(guided)
	for (j = 0; j < max_order; j++)
	{
		cs[j][j] = 0; //对角线上的值直接给0 反正用不到
		for (i = j+1; i < max_order; i++)
		{
			cs[i][j] = sqrt(((2.0*i-1)*(2.0*i+1))/((i-j)*(i+j)));
		}
	}
	return;
}

void gctl::get_b_nm_array(int max_order, array<array<double>> &cs)
{
	int i,j;
	if (cs.size() != max_order)
	{
		cs.resize(max_order);
		for (i = 0; i < max_order; i++)
			cs[i].resize(i+1);
	}

	//向下列推计算
#pragma omp parallel for private(i,j) schedule(guided)
	for (j = 0; j < max_order; j++)
	{
		cs[j][j] = 0; //对角线上的值直接给0 反正用不到
		for (i = j+1; i < max_order; i++)
		{
			cs[i][j] = sqrt(((2.0*i+1)*(i+j-1)*(i-j-1))/((i-j)*(i+j)*(2.0*i-3)));
		}
	}
	return;
}

void gctl::nalf_sfcm(array<array<double>> &nalf, const array<array<double>> &a_nm, 
	const array<array<double>> &b_nm, int max_order, double theta, 
	legendre_norm_e norm, bool derivative)
{
	if (a_nm.size() != max_order || b_nm.size() != max_order)
	{
		std::string err_str = "Incompatible coefficients' size.";
		throw runtime_error(err_str);
	}

	double norSum;
	if (norm == One)
	{
		norSum = 1.0;
	}
	else if (norm == Pi4)
	{
		norSum = 4.0*GCTL_Pi;
	}

	if (nalf.size() != max_order)
	{
		nalf.resize(max_order);
		for (int i = 0; i < max_order; i++)
			nalf[i].resize(i+1);
	}

	if (derivative)
	{
		double tmp;
		array<double> tmp_nalf(max_order, 0.0), tmp2_nalf(max_order, 0.0);

		nalf[0][0] = 0.0;
		tmp_nalf[0] = sqrt(norSum)/sqrt(4.0*GCTL_Pi);

		nalf[1][1] = sqrt(3.0)*cos(theta*GCTL_Pi/180.0);
		tmp_nalf[1] = sqrt(3.0)*sin(theta*GCTL_Pi/180.0);

		//计算对角线上的值 递归计算 不能并行
		for (int i = 2; i < max_order; i++)
		{
			nalf[i][i] = cos(theta*GCTL_Pi/180.0)*sqrt(0.5*(2.0*i+1)/i)*tmp_nalf[i-1] 
				+ sin(theta*GCTL_Pi/180.0)*sqrt(0.5*(2.0*i+1)/i)*nalf[i-1][i-1];

			tmp_nalf[i] = sin(theta*GCTL_Pi/180.0)*sqrt(0.5*(2.0*i+1)/i)*tmp_nalf[i-1];
		}

		//计算次对角线(m+1,m)上的值 递归计算 不能并行
		for (int i = 0; i < max_order-1; i++)
		{
			nalf[i+1][i] = -1.0*sin(theta*GCTL_Pi/180.0)*sqrt(2.0*i+3)*tmp_nalf[i]
				+ cos(theta*GCTL_Pi/180.0)*sqrt(2.0*i+3)*nalf[i][i];
			
			tmp2_nalf[i] = tmp_nalf[i];
			tmp_nalf[i] = cos(theta*GCTL_Pi/180.0)*sqrt(2.0*i+3)*tmp_nalf[i];
		}

		//这里可以使用并行加速计算外层循环 内层计算因为是递归计算因此不能并行
		int i,j;
#pragma omp parallel for private(i,j, tmp) schedule(guided)
		for (j = 0; j < max_order-1; j++)
		{
			for (i = j+2; i < max_order; i++)
			{
				nalf[i][j] = -1.0*a_nm[i][j]*sin(theta*GCTL_Pi/180.0)*tmp_nalf[j]
					+ a_nm[i][j]*cos(theta*GCTL_Pi/180.0)*nalf[i-1][j] - b_nm[i][j]*nalf[i-2][j];

				tmp = tmp_nalf[j];
				tmp_nalf[j] = a_nm[i][j]*cos(theta*GCTL_Pi/180.0)*tmp_nalf[j] - b_nm[i][j]*tmp2_nalf[j];
				tmp2_nalf[j] = tmp;
			}
		}
	}
	else
	{
		//赋初值给前两个对角线上的值
		//norSum为1时第一个值为sqrt(1)/sqrt(4.0*pi) = 1/sqrt(4.0*pi), 对应的归一化值为1
		//norSum为4.0*pi时第一个值为4.0*pi/sqrt(4.0*pi) = 1, 对应的归一化值为4.0*pi
		nalf[0][0] = sqrt(norSum)/sqrt(4.0*GCTL_Pi);
		nalf[1][1] = sqrt(3.0)*sin(theta*GCTL_Pi/180.0);
		
		//计算对角线上的值 递归计算 不能并行
		for (int i = 2; i < max_order; i++)
		{
			nalf[i][i] = sin(theta*GCTL_Pi/180.0)*sqrt(0.5*(2.0*i+1)/i)*nalf[i-1][i-1];
		}
		
		//计算次对角线(m+1,m)上的值 递归计算 不能并行
		for (int i = 0; i < max_order-1; i++)
		{
			nalf[i+1][i] = cos(theta*GCTL_Pi/180.0)*sqrt(2.0*i+3)*nalf[i][i];
		}

		//这里可以使用并行加速计算外层循环 内层计算因为是递归计算因此不能并行
		int i,j;
#pragma omp parallel for private(i,j) schedule(guided)
		for (j = 0; j < max_order-1; j++)
		{
			for (i = j+2; i < max_order; i++)
			{
				nalf[i][j] = a_nm[i][j]*cos(theta*GCTL_Pi/180.0)*nalf[i-1][j] - b_nm[i][j]*nalf[i-2][j];
			}
		}
	}
	return;
}